1. Field of the Invention
The present invention relates to a dressing apparatus for use with a polishing apparatus for polishing a work object to be polished, such as a semiconductor wafer, which is used to regenerate a polishing surface of a polishing table.
2. Related Arts
With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit wiring patterns have been becoming increasingly fine and, as a result, spaces between wiring patterns have also been decreasing. As wiring spacing decreases to less than 0.5 microns, the depth of focus in circuit pattern formation in photolithography or the like becomes shallower. Accordingly, surfaces of semiconductor wafers on which circuit pattern images are to be formed by a stepper are required to be polished by a polishing apparatus to an exceptionally high degree of surface flatness, and a polishing process using a polishing apparatus is conducted as one method for obtaining such surface flatness.
A polishing apparatus of this kind generally comprises a polishing table on which a polishing cloth is provided to form a polishing surface, and a top ring for holding a substrate (object to be polished) with a surface thereof (to be polished) being orientated towards the polishing table. The substrate is urged against the polishing table under a predetermined pressure exerted by the top ring while rotating the top ring and the polishing table so that the surface of the substrate is polished to have a flat and mirror-finish surface while a polishing liquid is supplied.
A dressing apparatus is disposed aside the polishing table, and, by rotating the dressing apparatus and the polishing table while urging a flat dressing surface of the dressing apparatus against the polishing surface of the polishing table, any polishing liquid and abraded particles adhering to the polishing surface are removed and the polishing surface is normalized.
The dressing surface of the dressing apparatus comprises particles such as diamond particles which are adhered to the lower surface of a dresser by means of electrical deposition. However, during the dressing, some particles detach from the dressing surface and remain on the polishing surface of the polishing table, with the result that scratches are formed on the substrate. Further, in such a dresser, since diamond particles are usually adhered by electrical deposition in the form of a single layer, detachment and deterioration of the particles tends to occur, which necessitates the frequent exchange or replacement of the dresser itself. This is a time-consuming and costly operation.
The present invention aims to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a dressing apparatus in which a polishing surface can be regenerated for a long period without any danger of scratching an object to be polished.
According to a first aspect of the present invention, there is provided a dressing apparatus in which a dressing surface of a dresser is urged in a sliding motion against a polishing surface, the dressing surface being formed from grindstone.
The grindstone is formed by binding abrasive particles having a particle diameter of 1 micrometer or less by means of a predetermined binder to obtain a layer having a predetermined thickness. Since the abrasive particles have a small diameter, even if the abrasive particles remain on the polishing surface of the polishing table, an object to be polished (substrate) can be prevented from being damaged by the abrasive particles. It is preferable that strength of the binder be selected so that the abrasive particles can be held in opposition subject to whatever force is applied during a dressing operation, and that such a binder strength be adjusted in accordance with the selection of a material and setting of a void ratio.
By setting the strength and property of the binder so that the binder is gradually denuded to form a new dressing surface as the dressing operations progress, a dresser having a long service life can be provided. As the dressing grindstone, a grindstone may have a so-called xe2x80x9cabrasive particle self-generating functionxe2x80x9d formed by binding polishing particles by means of a binder having certain dissolving or destroying ability so that the abrasive particles are regenerated due to dissolution or destruction of the binder may be used.
According to a second aspect of the present invention, in the dressing apparatus according to the first aspect, a grindstone configuration correcting mechanism for maintaining a flat dressing surface is further provided, whereby the dressing surface of the grindstone is reoriented as necessary, to maintain a constant surface configuration.
According to a third aspect of the present invention, in the dressing apparatus according to the first or second aspect, the dressing surface is provided with a number of grooves or minute holes. By this arrangement, an abrasive particle removing function during dressing can be enhanced, a lubricating and cooling function of the dressing liquid for the dressing surface can also be enhanced, and, a surface tension force during the separation of the grindstone from the polishing table or the grindstone configuration correcting machine can be reduced to facilitate separation.
According to a fourth aspect of the present invention, there is provided a polishing apparatus comprising a polishing table having a polishing surface, a substrate holding member for holding a substrate and for urging the substrate against the polishing surface, and a dressing apparatus according to any one of the first to third aspects.
According to a fifth aspect of the present invention, in the polishing apparatus according to the fourth aspect, a fluid injecting mechanism for injecting fluid onto the polishing surface of the polishing table or the dressing surface of the dresser is further provided. By this arrangement, fluid is supplied between the grindstone and the polishing surface of the polishing table by the fluid injecting mechanism, thereby reducing the surface tension force between the grindstone and the polishing surface so as to facilitate separation of the grindstone from the polishing surface.
According to a sixth aspect of the present invention, in the polishing apparatus according to the fourth aspect, a residual abrasive particle cleaning nozzle for removing from the polishing table abrasive particles which have become detached from the grindstone is disposed in the vicinity of the polishing table. By this arrangement, any residual abrasive particles can be quickly removed.